Method of manufacturing cushion for front passenger seat air bag device

ABSTRACT

A cushion of a passenger airbag device that is reduced in volume and shows a stable behavior when inflated and deployed is achieved. The present invention is a method of producing a cushion ( 10 ) of a passenger airbag device ( 1 ) having a portion with a desired curvature by sewing side edges of base fabric pieces constituting a main panel ( 12 ) and left and right side panels ( 14 ) together. The main panel ( 12 ) and the side panels ( 14 ) are sewn together so as to form a rectangular opening, whose short sides have a length equal to the width of the side panels ( 14 ) and whose long sides have a length equal to the width of the main panel ( 12 ), at a position where stitches in the main panel ( 12 ) and side panels ( 14 ) start or end. Then, the portion with a desired curvature is formed by folding the short sides toward the opening and sewing the short sides and the long sides together.

TECHNICAL FIELD

The present invention relates to a method of producing a cushion of anairbag device, and more specifically, it relates to a method ofproducing a cushion of a passenger airbag device.

BACKGROUND ART

In general, a passenger airbag device is stored in an instrument panelof a vehicle. When the vehicle stops abruptly due to a collision or thelike, the passenger airbag device receives a supply of gas from aninflator attached to the airbag device, is inflated through a deploymentdoor provided in a top surface of the instrument panel, and is deployedin a space between a windshield (front window) and an occupant seated ina passenger's seat, thereby protecting the occupant seated in thepassenger's seat.

This passenger airbag device is in contact with the windshield and thetop surface of the instrument panel when it is inflated and deployed,whereby the behavior thereof is stabilized. However, if the instrumentpanel is designed to have a small portion on the occupant side, withrespect to an installation position of the airbag device, in the topsurface of the instrument panel, the behavior of a cushion (bag) of theairbag device is unstable.

To solve this problem, the volume of the cushion has to be increased tofill a space surrounded by the occupant, the windshield of the vehicle,and the instrument panel, thereby reliably receiving the occupant. Thus,cushions of passenger airbag devices tend to have large volumes.

A cushion of an airbag device having a large volume requires a lageramount of base fabric constituting the cushion. Furthermore, for quickinflation and deployment of the cushion having a large volume, ahigh-power inflator is needed.

However, because high-power inflators are expensive, the use of such aninflator increases the total cost. In addition, the strength of theairbag device and components thereof also needs to be increased to copewith the power of the inflator, resulting in a problem in that theweight of the airbag device increases.

To overcome this problem, a passenger airbag device, in which the volumeof the cushion is reduced so that it can be quickly inflated by arelatively low-power inflator while exhibiting sufficientimpact-absorbing ability, has been proposed (see PTL 1).

FIG. 7 shows an example of such a passenger airbag device.

A cushion 100 of this passenger airbag device includes anoccupant-facing surface 102 at its front end, and a windshield-facingsurface 104 at an upper surface thereof. The occupant-facing surface 102and the windshield-facing surface 104 are configured to be connected byan inner member 106. Therefore, when an inflator 112 is activated todischarge gas, the occupant-facing surface 102 is inflated toward theoccupant due to the pressure of the gas, and a middle portion of thewindshield-facing surface 104 in the top-bottom direction is pulled bythe occupant-facing surface 102 through the inner member 106 and isdeployed in a shape recessed toward the inner side of the cushion awayfrom the windshield 122. With this configuration, the volume of thecushion 100 is reduced.

Similarly, although it is not necessarily aimed at reducing the volumeof the cushion of an airbag device, a passenger airbag device having acushion composed of a first inflation portion, which constitutes anoccupant protection portion that can interfere with an occupant seatedin a passenger's seat, and a second inflation portion, which is inflatedbetween the first inflation portion and the instrument panel with theinflation gas flowing from the first inflation portion when the firstinflation portion is inflated, is known (see PTL 2).

However, because the cushion 100 of the airbag device disclosed in PTL 1is reduced in volume on the windshield side, the behavior of the cushion100 when deployed may be less stable. Furthermore, because a separatemember, i.e., the inner member 106, is required and because an operationto attach the inner member 106 to the occupant-facing surface 102 andthe windshield-facing surface 104 is required, the fabrication processbecomes complex, resulting in another problem in that the cost isincreased compared with a cushion formed by simply joining the basefabric pieces.

Furthermore, although the passenger airbag device disclosed in PTL 2 hasa more complex structure than that disclosed in PTL 1 and requires highcost, it does not always succeed in reducing the volume of the cushionof the airbag device.

If the overall volume of the cushion is simply reduced, as shown in, forexample, FIG. 8, the cushion 10 starts to be inflated and deployed fromthe top surface of the instrument panel 20, is deployed along the topsurface of the instrument panel 20 toward the occupant, withoutcompletely filling the space between the instrument panel 20 and thewindshield 25 (see FIGS. 8A to 8D). In the subsequent process of beinginflated and deployed, the cushion 10 temporarily hangs down in front ofthe instrument panel 20 (see FIG. 8E) but is then erected away from thepanel surface upon further application of the gas pressure from theinflator (see FIG. 8F). Therefore, the behavior of the cushion 10 isunstable, and sufficient support may not be provided because the supportposition of the cushion 10 when the occupant moves forward into thecushion 10 is unstable.

Hence, a passenger airbag device that shows a stable behavior wheninflated and deployed and has a sufficient impact-absorbing abilitywhile reducing the volume of the cushion has been required. Theapplicant, in view of the above-described circumstances, has developed apassenger airbag device that includes a belt-like main panel having asurface facing an occupant, and left and right side panels joined toside edges of the main panel, and that has a projecting portion on aback surface side of a cushion, as viewed from the occupant.

In this passenger airbag device, when the cushion is inflated anddeployed, the projecting portion of the cushion is supported by a frontsurface of an instrument panel. Thus, even if the cushion of thepassenger airbag device is reduced in volume, the behavior thereof isstabilized.

However, when sewing the base fabric pieces constituting the main paneland the side panels, if ends of the main panel are sewn together first,and then, side edges of the side panels are laid on the side edges ofthe main panel and sewn thereto, any relative misalignment between thebase fabric pieces occurring during sewing cannot be absorbed. As aresult, wavy wrinkles (crinkles) are formed at the seam, resulting in aproblem of gas leakage or, in an extreme case, breakage of that portionwhen gas from the inflator is injected.

In particular, when a stitch is sewn along a joining line having a smallcurvature, the misalignment between the base fabric pieces constitutingthe main panel and the side panels is likely to occur. However, becausethe above-described projecting portion, for example, needs to be formedin a shape having a considerably smaller curvature than the otherportions, the above-described projecting portion, for example, cannot beformed by using the above-described sewing method.

CITATION LIST Patent Literature

-   PTL 1: Japanese Unexamined Patent Application Publication No.    2002-19560-   PTL 2: Japanese Unexamined Patent Application Publication No.    2005-329749

SUMMARY OF INVENTION Technical Problem

The present invention has been made to solve this problem, and an objectthereof is, by employing a new sewing method capable of absorbing anymisalignment between the base fabric pieces, to enable a portion with adesired curvature to be formed in the cushion, thereby reducing thevolume of the cushion of a passenger airbag device and thereby realizinga passenger airbag device that shows a stable behavior when inflated anddeployed and has a sufficient impact-absorbing ability.

Solution to Problem

(1) A method of producing a cushion of a passenger airbag device of thepresent invention is a method of producing a cushion of a passengerairbag device having a portion with a desired curvature by sewing sideedges of base fabric pieces constituting a main panel and left and rightside panels. The method includes a step of sewing the main panel and theside panels together so as to form a rectangular opening, whose shortsides have a length equal to the width of the side panels and whose longsides have a length equal to the width of the main panel, at a positionwhere stitches in the main panel and side panels start or end; and astep of forming the portion with a desired curvature by folding theshort sides toward the opening and sewing the short sides and the longsides together.

(2) In the method of producing a cushion of a passenger airbag device ofthe present invention described in the above (1), the cushion has, on aninstrument panel side thereof in an inflated and deployed state, aprojecting portion that functions as support means when an occupantmoves forward therein, and the portion with a desired curvature is theprojecting portion.

(3) In the method of producing a cushion of a passenger airbag device ofthe present invention described in the above (1), the cushion, in aninflated and deployed state, has a shape corresponding to a spacebetween a windshield and a top surface of the instrument panel so as tofill the space, and the portion with a desired curvature is the portionhaving a shape corresponding to the space.

ADVANTAGEOUS EFFECTS OF INVENTION

According to the present invention, by sewing the main panel and theside panels together by following the new sewing process, a portion witha desired curvature can be formed in the cushion. For example, byforming a projecting portion that serves as support means when thecushion is inflated and deployed, it is possible to realize a passengerairbag device that has a smaller volume compared with typical existingcushions of passenger airbag devices and that can be inflated anddeployed in a stable manner regardless of the design of the instrumentpanel, in which the passenger airbag device is to be installed, or thelayout of the vehicle.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a perspective view of a cushion of a first passenger airbagdevice produced by a production method of the present invention, in aninflated state.

FIG. 2 is a side view of the cushion in an inflated state, showing astate before an occupant moves forward therein.

FIG. 3 is a side view showing the occupant moving forward into thecushion in an inflated state.

FIG. 4 includes schematic views for describing the behavior of thecushion in an inflated and deployed state.

FIG. 5 is a side view of a cushion of a second passenger airbag devicein an inflated and deployed state.

FIG. 6 includes diagrams for describing a method of producing a cushionof a passenger airbag device according to an embodiment of the presentinvention.

FIG. 7 shows an example of an existing passenger airbag device.

FIG. 8 includes schematic views for describing the behavior of a cushionaccording to Comparative Example, in an inflated and deployed state.

DESCRIPTION OF EMBODIMENTS

Before describing a production method of the present invention, first, apassenger airbag device having a cushion that can be produced byemploying a sewing method according to the present invention, that is, apassenger airbag device that shows a stable behavior when inflated anddeployed and has a sufficient impact-absorbing ability while reducingthe volume of the cushion thereof, will be described.

FIG. 1 is a perspective view of a cushion 10 of the passenger airbagdevice in an inflated state. FIG. 2 is a side view of the cushion 10 inan inflated state, showing a state before an occupant moves forwardtherein.

The cushion 10 of the passenger airbag device 1 includes three pieces,i.e., a main panel 12 and side panels 14, and has a configuration inwhich the side panels 14 are attached to side edges of the main panel12, forming a single component. The main panel 12 has an opening 15 towhich an inflator is attached.

As shown in FIG. 2, the cushion 10 includes, on an instrument panel sideas viewed from the occupant side (hereinbelow, simply, “back surfaceside”), an attaching portion 10 a to which an inflator 30 is to beattached; a projecting portion 10 b that comes into contact with a sidesurface of the instrument panel; a depressed portion or a recess 10 cformed adjacent to the projecting portion 10 b and between the attachingportion 10 a and the projecting portion 10 b; and a recess 10 d providedadjacent to and below the projecting portion 10 b. The other side of therecess 10 d is continuous with the occupant side or the surface side,and the occupant-facing surface constitutes a smooth surface thatreduces the impact exerted when the occupant moves forward therein.

The side panels 14 are cut into a shape having portions corresponding tothe projecting portion 10 b, the recess 10 c, and the recess 10 d torealize a back surface shape of the cushion 10 of the passenger airbagdevice 1.

The left and right side panels 14, cut into the above shape, are joinedto the side edges of the main panel 12 by, for example, sewing, therebyforming the cushion 10.

Herein, the projecting portion 10 b of the cushion 10 is a portion witha desired curvature different from the other portions of the cushion 10(herein, a portion having a considerably smaller curvature than theother portions). The tip thereof comes into contact with a front surface22 of the instrument panel 20 when the cushion 10 is inflated anddeployed, and the projecting portion 10 b constitutes a support portionof the cushion 10 that receives the occupant moving forward therein.

FIG. 3 is a side view showing the occupant moving forward into thecushion 10. In FIG. 3, forces acting when the occupant moves forwardinto the cushion are illustrated in a decomposed manner.

As shown in FIG. 3, when the gas from the inflator 30 is supplied to thecushion 10, the cushion 10, as will be shown in FIG. 5 mentioned below,is inflated on the instrument panel 20 by a gas jet and is deployedoutward. When the cushion 10 has been deployed outward beyond the topsurface of the instrument panel 20, the cushion 10 is then deployeddownward under the influence of its own weight, and the projectingportion 10 b comes into contact with the front surface 22 of theinstrument panel 20. Once the projecting portion 10 b comes into contactwith the front surface 22 of the instrument panel 20, the second recess10 d restricts the inflation and deployment of the cushion 10 downward.The projecting portion 10 b is kept in contact with the front surface 22of the instrument panel 20 due to the gas pressure from the inflator.Thus, the position of the cushion 10 in an inflated and deployed statecan be stabilized.

Reference signs F1 to F3 in FIG. 3 represent the relationship betweenforces applied to the cushion 10 when the occupant moves forward intothe cushion 10 in an inflated and deployed state, as above.

More specifically, reference sign F1 represents the vector (magnitudeand direction) of a force applied to the cushion 10 when an occupant'shead moves forward into the cushion 10. Reference sign F2 represents thevector of gravity acting on the cushion 10. Reference numeral F3represents the vector of a resultant force of the vectors F1 and F2, inother words, the direction and magnitude of the force actually appliedto the cushion 10 when the occupant moves forward into the cushion 10 inan inflated and deployed state.

It is preferable that the projecting portion 10 b be formed so as toextend in the direction of the vector F3, taking into consideration thevector F3, of this force. By doing so, when the occupant moves forwardinto the cushion 10, that force is directly transmitted to the frontsurface of the instrument panel 20 through the projecting portion 10 b,and, as a result of that force being balanced with the drag force, thecushion 10 can reduce the impact applied to the occupant due to acollision, in a stable manner (i.e., without moving arbitrarily).

Note that, if the position of the projecting portion 10 b is misalignedwith the direction of the vector F3, when the occupant moves forwardinto the cushion 10 of the passenger airbag device 1, a rotation momentdue to the vector F3, of the force is generated in the cushion 10, ataround a contact point between the projecting portion 10 b and theinstrument panel 20. Thus, the cushion 10 moves arbitrarily andtherefore cannot reduce the impact in a stable state.

Conversely, if the vector F3, of the force acting when the occupantmoves forward into the cushion 10 is identified, because portions on theback surface side of the cushion 10 other than a portion subjected tothe vector F3, i.e., portions other than the projecting portion 10 b,are obviously not involved in the transmission of the force, suchportions need not be brought into contact with the instrument panel 20,and consequently, it is understood that the volume of these portions canbe reduced.

Hence, in this passenger airbag device, portions other than theprojecting portion 10 b are cut away so that these portions are recessedinward as much as possible, while the projecting portion 10 b of thecushion 10 is brought into contact with the surface of the instrumentpanel 20. With this configuration, the behavior of the airbag device inan inflated and deployed state is stabilized, and the volume of thecushion 10 is reduced.

In the passenger airbag device 1, by reducing the volume of the cushion10, the power of the inflator can be reduced relatively, and the size ofthe side panels 14 constituting the cushion 10 can also be reducedrelatively. As a result, the cost can be reduced. Furthermore, becausethe cushion 10 is reduced in volume on the back surface side and lowersurface side thereof, there is no possibility of its behavior, wheninflated and deployed, being unstable due to lack of support by thewindshield 25.

Although the direction in which the projecting portion 10 b of thecushion 10 extends is aligned with the direction of the vector F3 whenthe occupant moves forward into the cushion 10, the position, in thecushion 10 of the passenger airbag device 1, at which the occupantactually moves forward therein varies depending on the height andposture of the occupant. Therefore, the direction of the vector F3 needsto have a certain width (tolerance).

The actually required width can be determined based on results ofexperiments conducted with respect to assumed occupants' heights andpostures. In actuality, the width of the projecting portion 10 b isobtained by multiplying a value range obtained from the results ofexperiments by a predetermined factor of safety.

FIGS. 4A to 4F are schematic views for describing the behavior of thecushion 10 of the passenger airbag device 1 in an inflated and deployedstate.

A process is shown in which the cushion 10 starts to be inflated anddeployed from a predetermined position of the top surface of theinstrument panel 20 and continues to be deployed upward and rightward inthe figures while being restricted between the windshield 25 and the topsurface of the instrument panel 20 (see FIGS. 4A to 4C). As the lowersurface of the cushion 10 extends outward beyond the top surface of theinstrument panel 20, the projecting portion 10 b moves downward, whilemaking contact with the front surface of the instrument panel 20 (seeFIGS. 4D and 4E), and stays at that position (FIG. 4F).

As is clear from the comparison between the cushion 10 according to thisembodiment and the cushion 10 shown in FIG. 8, which is simply reducedin volume without providing the projecting portion 10 b, because thecushion 10 has the projecting portion 10 b on the back surface thereof,when it has been deployed outward beyond the instrument panel 20, theprojecting portion 10 b is then deployed downward and comes into contactwith the front surface 22 of the instrument panel 20. Thus, the cushion10 is not erected away from the surface of the instrument panel, asshown in FIG. 8.

As has been described above, in the passenger airbag device 1, thevolume of the cushion 10 is reduced not by using a component other thanthe base fabric pieces, as required in an existing system, but simply bysewing the side panels 14, which have been cut into a shape with adesired curvature portion so as to form the projecting portion 10 b, tothe edge of the main panel 12. Thus, the production cost can be reduced.

Furthermore, because the cushion 10, even without the support by thewindshield 25 during inflation and deployment, is deployed outward andthen downward when it has extended beyond the top surface of theinstrument panel 20, as described above, and because the tip of theprojecting portion 10 b comes into contact with the surface of theinstrument panel 20 at a relatively early stage of the deployment and ismaintained in that state, the behavior thereof in a deployed state canbe stabilized.

Next, a second passenger airbag device to which the production method ofthe present invention is applied will be described.

FIG. 5 is a side view of the cushion 10 of the second passenger airbagdevice 1, in an inflated and deployed state.

The cushion 10 comes into contact with the windshield 25 as it isinflated and deployed, and the behavior thereof is stabilized by beingin contact with the windshield 25 and the top surface of the instrumentpanel 20. A portion of the cushion 10 to be deployed between thewindshield 25 and the top surface of the instrument panel 20 is formedin a shape corresponding to the shape of the space therebetween, and theshape of the other part is the same as that of the passenger airbagdevice 1.

With this configuration, the volume of the cushion 10 of the secondpassenger airbag device 1 can be further reduced, compared with thecushion 10 of the first passenger airbag device 1. More specifically,because the portion of the cushion 10 between the windshield 25 and thetop surface of the instrument panel 20 is formed in a shapecorresponding to the shape of the space therebetween, an excess partthat does not fit in the space between these portions does not protrudeand swell out toward the occupant side. Thus, not only can the power ofthe inflator be further reduced, but also can the size of the sidepanels 14 be further reduced. Accordingly, a further cost reduction ispossible.

Next, an embodiment of a method of producing the above-describedpassenger airbag device will be described with reference to thedrawings.

The passenger airbag device to be produced has already been describedabove and is formed of the main panel 12 and the left and right sidepanels 14.

FIGS. 6A to 6D are diagrams showing a sewing process according to theembodiment of the present invention.

FIG. 6C is an enlarged view of the relevant part (a rectangular portionS) in FIG. 6B.

In this sewing process, the main panel 12 and the side panels 14, cutinto a shape including a small curvature portion, such as theabove-described projecting portion, and a straight portion 14 a at thetip thereof, are sewn together along their edges (see FIGS. 6A and 6B).At this time, ends of the main panel 12, as well as a stitch-startingend and a stitch-terminating end in the main panel 12 and side panels14, are not sewn together. By doing so, the ends of the main panel 12are not bound by each other at the stitch-starting end andstitch-terminating end, and a rectangular portion S, in which thestraight portions 14 a constitute short sides and long sides have alength equal to the width of the main panel 12, is left as an unsewnportion (see FIG. 6C).

Then, the short sides of the unsewn rectangular portion S, i.e., thestraight portions 14 a of the side panels 14, are folded inward of therectangular shape in a V-shape and closed (see FIG. 6D), and the closedportion is sewn together (see FIG. 6E).

By using this sewing method, even if the main panel 12 and the left andright side panels 14 are displaced with respect to one another duringsewing, because such displacement occurring during sewing is adjustedwhen the short sides (straight portions 14 a) of the unsewn rectangularportion are folded inward in a V-shape and sewn, the seams do not becomewavy.

Accordingly, portions having small curvatures (irregular-shapeportions), such as the projecting portion 10 b of the cushion 10 and theportion between the windshield 25 and the top surface of the instrumentpanel 20, can be formed without taking into consideration the radius ofcurvature.

Note that a plurality of irregular-shape portions can be formed in themain panel 12. In such a case, the main panel 12 is formed of aplurality of panels.

REFERENCE SIGNS LIST

-   1: passenger airbag device,-   10: cushion,-   10 b: projecting portion,-   10 c and 10 d: recess,-   12: main panel,-   14: side panels,-   20: instrument panel, and-   25: windshield.

1. A method of producing a cushion of a passenger airbag device having aportion with a desired curvature by sewing side edges of base fabricpieces constituting a main panel and left and right side panels, themethod comprising: a step of sewing the main panel and the side panelstogether so as to form a rectangular opening, whose short sides have alength equal to the width of the side panels and whose long sides have alength equal to the width of the main panel, at a position wherestitches in the main panel and side panels start or end; and a step offorming the portion with a desired curvature by folding the short sidestoward the opening and sewing the short sides and the long sidestogether.
 2. The method of producing a cushion of a passenger airbagdevice according to claim 1, wherein the cushion has, on an instrumentpanel side thereof in an inflated and deployed state, a projectingportion that functions as support means when an occupant moves forwardtherein, and wherein the portion with a desired curvature is theprojecting portion.
 3. The method of producing a cushion of a passengerairbag device according to claim 1, wherein the cushion, in an inflatedand deployed state, has a shape corresponding to a space between awindshield and a top surface of the instrument panel so as to fill thespace, and wherein the portion with a desired curvature is the portionhaving a shape corresponding to the space.